From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 29DF4C43381 for ; Tue, 5 Mar 2019 14:53:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EAEE520842 for ; Tue, 5 Mar 2019 14:53:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="ow9VBWH8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727751AbfCEOxk (ORCPT ); Tue, 5 Mar 2019 09:53:40 -0500 Received: from merlin.infradead.org ([205.233.59.134]:32830 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726250AbfCEOxj (ORCPT ); Tue, 5 Mar 2019 09:53:39 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=CmAIyH+dAiiqoSUSc0kf2M2hNfWk2Q0D9uVzdk9oRNg=; b=ow9VBWH8Yz9vW4jkNKTkmEDkC 3pGeTCxjp6qSQ5Co5PBJR5tA72XqWlJk+NNz8fcU5K7qmiQJSOAveB4zW3Ngnbqt5VXP14eJAtFsl 8F+l4UfDE+JvMYi68bv51oWv2Qt/rXqvCYLAzSDiGmec25t2KpWLBrxuE/CbtHqH/gC02xTThKu6z R3fN4FCtyPReNnG3+inI9TC0BYR8I7HuNzbGG9yAM/IeNXExXuyHVUiAn7emXl1UGdZi8QybCcLEr NpJ8XXt/rr2cCh3OUFtbnSkinTZAH5tB8z3y+D3AlgAL9kTMczWm0SzBjA2ic51AT2B3w+GF9RMxl 9c6HfcD+w==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1h1BRM-0007Bb-RN; Tue, 05 Mar 2019 14:53:09 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 7FDD920288BA2; Tue, 5 Mar 2019 15:53:06 +0100 (CET) Date: Tue, 5 Mar 2019 15:53:06 +0100 From: Peter Zijlstra To: Masami Hiramatsu , g@hirez.programming.kicks-ass.net Cc: Linus Torvalds , kernel test robot , Steven Rostedt , Shuah Khan , Linux List Kernel Mailing , Andy Lutomirski , Ingo Molnar , Andrew Morton , Changbin Du , Jann Horn , Kees Cook , Andy Lutomirski , Alexei Starovoitov , Nadav Amit , Joel Fernandes , yhs@fb.com, lkp@01.org Subject: Re: [uaccess] 780464aed0: WARNING:at_arch/x86/include/asm/uaccess.h:#strnlen_user/0x Message-ID: <20190305145306.GL32477@hirez.programming.kicks-ass.net> References: <155136980507.2968.15165201054223875356.stgit@devbox> <20190303173954.kliegojbuigqi5tn@inn2.lkp.intel.com> <20190304101434.8429ffffb17813c0e7930130@kernel.org> <20190304180610.2d4f6f08d9ad89d6abae3597@kernel.org> <20190305113635.18f80ea3b1f4fca54b9d21e4@kernel.org> <20190305090729.GF32477@hirez.programming.kicks-ass.net> <20190305225801.a63ac8712105ab2e673be1bc@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190305225801.a63ac8712105ab2e673be1bc@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 05, 2019 at 10:58:01PM +0900, Masami Hiramatsu wrote: > Could you tell me why WARN_ON_ONCE(!in_task()) is needed in access_ok()? That came from here: lkml.kernel.org/r/20190225145240.GB32534@hirez.programming.kicks-ass.net Because in-irq usage is dodgy, since we don't actually know what mm or ds it loaded. > > I dislike that whole KERNEL_DS thing, but obviously that's not something > > that's going away. > > > > Would something like: > > > > WARN_ON_ONCE(!(in_task || segment_eq(get_fs(), USER_DS))) > > > > Work? Then we allow KERNEL_DS in task context, but for interrupt and > > others require USER_DS. > > But what would this mean? I can't understand why we limit using > access_ok() so strictly and narrow the cases. Because it's been a source of bugs. Any sanity checking we can put in seems like a good thing at this point.